1. Field of the Invention
The invention relates methods of manufacture, particularly of printers and of droplet deposition inkjet printers.
2. Related Technology
Inkjet printers are capable of ejecting a small droplet of fluid onto a substrate. The fluid has particular properties and while it is typically called an “ink”, it may be colourless and/or contain biological or some other functional component. The ability of inkjet printers to eject such a wide variety of “inks” means that the print heads, the part of the printer which ejects the ink, come in a number of different shapes and sizes. Some print heads have as few as 16 ejection elements while others may have over 2000.
An ejection element typically comprises a number of components. The first is an orifice or nozzle through which the droplet fluid is ejected towards the substrate. The second component is an ejection chamber that contains the fluid to be ejected. The third component is an actuator that pressurises the fluid in the chamber and effects the ejection of the fluid through the orifice. The actuators are typically mechanical or thermal. A further component is a fluid supply that supplies ink to the ejection chambers. The fluid supply may cause ink to flow continually through the ejection chamber.
Failure or errors in even a single ejection element may require the print head to be scrapped. Failures may occur in operation e.g. a permanent blockage in the orifice, damage to the nozzle plate etc. or during manufacture e.g. electrical faults or some other defect. It is well known that the greater the number of ejection elements the greater the statistical chance of that print head needing to be scrapped because of a fault. The manufacturing yield of large print heads can be low.
It has been proposed, to improve yield in larger print heads, to manufacture the print head from a plurality of smaller modules rather than from one large print head. Each module may be pre-tested before mounting onto a substrate enabling the overall yield of the large print head to be improved.
The modules must be capable of being manufactured to a high accuracy relative to one another. The high accuracy ensures that a first module provides the same functional capability as a second module in terms of, for example jet straightness, ejection speed etc. Modules should also have a high repeatability with respect to one another to allow a first module to replace a second module without significant re-alignment.
Techniques are proposed in the prior art to provide modules with such repeatability and accuracy. In WO 99/10179, repeatability is achieved by completing the print head and subsequently adhering a datum feature on the print head at a predetermined position relative to a nozzle or actuator. As each print head has a datum feature in the predetermined position relative to the nozzle it is possible to use the datum feature to locate the print head in the printer.
It will be appreciated that with this technique it can take some time to align each datum relative to the print head and additionally adds a further manufacturing step. The datum feature must be aligned in the printer to both a high repeatability and high accuracy.